This invention relates to a process to reduce the residual peroxide levels in crosslinked ethylene-propylene diene monomer (EPDM) elastomer material and to inhalation devices containing EPDM gaskets made by the inventive process.
Metered-dose inhalers are commonly used to deliver medicaments to the respiratory system, particularly asthma and allergy medicaments. When a metered-dose inhaler is filled with medicament and shaken, the EPDM components are in direct contact with the medicament. The medicament is thus exposed to any residual peroxides in the gasket material. Applicants have found that these residual peroxides can cause significant oxidative degradation of the medicament. The longer the medicament is stored in the metered-dose inhaler in contact with the EPDM material, the more degradation occurs. Thus, the concentration of medicament significantly diminishes with storage time in the metered dose inhaler. This causes non-uniformity in patient dosing, because different dosages of medicament will be delivered with one inhaler actuation depending on how long the medicament has been stored in the inhaler.
Applicants have considered various approaches to reduce residual peroxides. For example, the peroxide may be reduced by use of different peroxide crosslink initiators during elastomer formulation or optimization of the elastomer curing process. The advantage of the present invention is that residual peroxides can be virtually eliminated with relative ease without the need to modify elastomer formulations or curing conditions. This avoids the need to retool the elastomer production process or to submit new information to regulatory agencies because of a change in formulation. Furthermore, Applicants' invention may be used in conjunction with other methods to further reduce residual peroxide levels.